Flow control valves are valves that control the flow of a fluid such that the fluid flow rate of the fluid exiting the valve outlet can be adjusted between a minimum value and a maximum value by lifting a valve member from its seated position. An example of such a flow control valve is a fuel injection valve which delivers fuel into the combustion chamber of an engine by injection into the intake port of the engine cylinder or directly into the combustion chamber. Typically a liquid fuel like diesel or gasoline has been used for fuelling such compression ignition internal combustion engines, and more recently, cleaner burning gaseous fuels such as natural gas, pure methane, ethane, liquefied petroleum gas, lighter flammable hydrocarbon derivatives, hydrogen, or blends of such fuels have been used as substitutes of diesel or gasoline.
Some types of fuel injection valves can control valve member lift to adjust the quantity of fuel that is introduced into the combustion chamber according to the operational state of the engine. The “valve member lift” is defined herein as the displacement of the valve member away from a closed/seated position to an open position in which fuel is delivered through the fuel injection valve into the combustion chamber. When the pressure of the fuel delivery to the fuel injection valve is constant, and the opening between the valve member and the valve seat is the choke point in the fuel flow path, an increase in valve member lift generally corresponds to an increase in the quantity of fuel being injected by increasing the flow rate through the opening between the valve member and the valve seat. This is beneficial for the engine operation because, when the engine is idling, or at low loads, a smaller amount of fuel is required for operating the engine compared to when the engine is operating at high loads and the amount of fuel injected into the combustion chamber needs to be increased to match the increased power requirements.
An example of such fuel injection valves with an adjustable valve member lift are fuel injection valves actuated by a piezoelectric actuator. Piezoelectric actuators are known in the industry to allow control of the valve member lift at intermediate positions between the fully closed and the fully open positions of the valve. With piezoelectric, magnetostrictive and other strain-type actuators, because actuator displacement is a function of actuator length and there are practical dimensional limits for the size of the actuator, a much smaller valve member lift is achieved with such actuators compared to electromagnetic actuators. Accordingly, in some cases, strain-type actuators might not be sufficient for delivering the amount of fuel required for the optimum engine operation at high loads.
An electromagnetic actuator, for example a solenoid, is typically employed when bigger displacements of valve needles are needed. Some of the prior art patent literature discloses the use of solenoid actuators for achieving different valve member lifts. For example, United Kingdom patent application number 2,341,893 describes an assembly of two actuators that permits the lifting of the valve member to a first intermediate position governed by the stroke of the first electromagnetic actuator, a second intermediate position governed by the stroke of the second electromagnetic actuator and a fully lifted position achieved by the combined strokes of the first and second actuators.
Another solution for controlling the lift of the valve member of a flow control valve can be to limit the movement of the valve member by providing an end stop that comes into contact with valve member when the latter is moved into its lifted position. An example of such an arrangement is described in German patent application number 1911827 which employs an electromagnetically actuated end stop for limiting the movement of the valve member. The end stop is moved by the magnetic force of the electromagnet against the force of a spring which keeps the end stop in contact with the valve member and this allows the movement of the valve member over a predetermined lift which corresponds to the travel distance of the end stop. A disadvantage of such an arrangement is that the movement of valve member is not as precise as desired because of the oscillations introduced by the spring acting on the end stop when the valve member comes into contact with the end stop. As discussed in this patent application, these oscillations can be diminished by choosing a spring with a larger elastic constant.
While other solutions for achieving a variable lift of a valve member in a flow control valve have been achieved by using piezoelectric or magnetostrictive actuators or hydraulic or mechanic actuators, such solutions are more complex requiring a more precise control of the actuator.
While the solutions from the prior art mentioned above allow holding the valve member of a flow control valve at a few intermediate positions between the closed and open position there is still a need for a more simple and accurate solution for lifting the valve member of a flow control valve at discrete lift positions.